The marriage between Juan López de Lazarraga and his wife, María de Gamboa, founded the monastery of Bidaurreta at the beginning of the 16th century in Oñate. The church with a Latin cross layout stands adjacent to the monastic building and its interior, one can see on the left side of the altarpiece, a beautiful plateresque altarpiece from the first half of the 16 century. Originally it was the main altarpiece of the church, but in the 18th century it took the current place.
The structure of the altarpiece is clear. Over the predella there are two bodies divided into five columns that have niches topped with half shells. All the niches are decorated with relief's except those of the central column, of which no relief's have been conserved as of today and several sculptures have been placed in lieu of them.
In the predella there are figures of apostles, three in every column, each of them with their attribute: San Pedro with key, Santiago with crosier and pilgrim hat... the trios are crowned by heads of winged angels in typical plateresque style.
The images of the first body represent scenes from the new testament. From left to right: the Annunciation, the Visitation, the Nativity and the Adoration of the Kings. In the second body, 4 scenes with Adam and Eve as protagonists narrate the creation of man until the expulsion from Paradise. The altarpiece is crowned with an upper part where the Virgin, the Lord and San Juan form the group of Calvary.
The delicate carving of the figures, their rich decoration and polychrome make this altarpiece a jewel of the Gipuzkoan renaissance.